This invention relates to a coating composition for use in a steel drawing and ironing process. More particularly, this invention relates to a alkali soluble removable coating composition which can be used to successfully deep draw beverage containers from tin-free steel.
Beverage containers such as soda and beer cans have been formed by drawing and ironing steel or aluminum to form the beverage container. However, this drawing and ironing process places great stress on the metal to be drawn and ironed which has lead to the requirement that a lubricant composition be coated on the metal surface prior to the can forming operation. For steel cans, this lubricant composition has been a tin coating which was applied to the sheet steel at the mill. This tin coating is a sacrificial coating which allows the steel to be successfully drawn. There is no continuous tin coating after the drawing and ironing operation is completed. Due to the prices of tin, the use of tin as a sacrificial coating for drawing and ironing steel beverage containers has become impractical, and a search has been conducted for a removable coating which can be easily and simply applied to black plate steel to allow the same to be drawn and ironed into beverage containers.
Leon Lewis, from U.S. Steel, has discovered a removable coating composition and a method for applying this coating to black plate steel, to enable the same to be successfully drawn and ironed. This composition comprises approximately 28% molybendum disulfide, approximately 58% of an aqueous floor polish composition, and approximately 14% of a wax emulsion drawing compound. This composition, although it allows cans to be drawn and ironed, has substantial coating and application problems and also is not stabile and tends to separate unless it is continuously stirred.